Catalytic hydrogenation of polymers containing double bonds

ABSTRACT

A process for the catalytic hydrogenation of polymers containing double bonds by the action of hydrogen on a solution of the polymer in an inert organic solvent in the presence of a catalyst complex comprising: A. a compound of iron, cobalt or nickel, B. an organo-aluminum compound, and C. a hexa-alkylphosphoric acid triamide of the general formula OP(NR2)3 in which R stands for alkyl of from one to four carbon atoms, the catalyst components A and B being used in a molar ratio of from 1 : 40 to 1 : 1 and the components A and C in a molar ratio of from 1 : 0.5 to 1 : 100.

waited States Patent Bronstert et al.

[ 1 .Eune 27, 1972 [54] CATALYTIC HYDROGENATHON 0F POLYMERS CONTAININGDOUBLE BONDS [72] Inventors: Klaus Bronstert, Carlsberg; VolkerLadenberger; Gerhard Fahrbach, both of Schwetzingen, all of Germany [73]Assignee: Badische Anllln- & Soda-Fahrik Aktiengesellschaft,Ludwigshafen/Rhine, Germany [22] Filed: Jan. 29, 1971 [21] Appl. No.:111,137

[30] Foreign Application Priority Data March 20, 1970 Germany ..P l9 13263.2

[52] US. Cl ..260/880 B, 260/82.1, 260/83.3, 260/83.5, 260/85.l,260/94.7 l-l, 260/96 l-lY,

[51] Int. Cl. ..C08d 5/00, C08d 5/02, C08f 27/24 [58] Field olSearch..260/94.7 H,94.9 l-l,96 l-l,85.1

[56] References Cited UNITED STATES PATENTS 3,541,064 11/1970 Yoshimotoet al ..260/85.1

Primary Examiner.lames A. Seidleck Assistant Examiner-William F. HamrockAttorney.l0hnst0n, Root, O'Keeffe, Keil, Thompson & Shurtleff 5 7]ABSTRACT in which R stands for alkyl of from one to four carbon atoms,the catalyst components A and B being used in a molar ratio of from 1 40to l l and the components A and C in a molar ratio offrom 1 20.5 to l100.

2 Claims, No Drawings CATALYTIC HYDROGENATION F POLYMERS CONTAININGDOUBLE BONDS This invention relates to a process for the hydrogenationof polymers containing double bonds in solution and in the presence of acatalyst complex comprising:

A. a compound of iron, cobalt or nickel,

B. an organo-aluminum compound, and

C. hexa-alkylphosphoric acid triamide as activator.

Polymers of diene hydrocarbons contain double bonds in the moleculechain. These double bonds may be hydrogenated by conventional processes.Products which are wholly or partly hydrogenated in this way aresuperior to nonhydrogenated polymers in that they possess improvedresistance to aging and are particularly resistant to oxidativedegradation. in the case of block copolymers of dienes and vinylaromatic compounds, in particular, the hydrogenated products also showimproved tensile properties and mechanical strength. When only partiallyhydrogenated, the diene polymers may be vulcanized. Such vulcanizatespossess a higher tensile strength and a lower glass temperature thanvulcanizates of non-hydrogenated diene polymers.

The catalytic hydrogenation of diene polymers in solution is known. In aprocess described in German Published application DAS No. 1,215,372 thehydrogenating catalyst consists of A. an organic compound of a metal ofsub-group VIII of the Periodic Table, and

B. a metal hydrocarbon compound.

German Published Patent application DAS No. 1,811,037 discloses ahydrogenation process in which the catalyst consists of A. an organiccompound of nickel or cobalt, and

B. a lithium, magnesium or aluminum-alkyl compound.

We have found that the rate of hydrogenation of polymers containingdouble bonds in inert organic solvents is greatly increased when acatalyst complex consisting of A. a compound of iron, nickel or cobalt,and

B. an organo-aluminum compound is used and there is added thereto C. ahexa-alkylphosphoric acid triamide as activator.

The activator has the general formula:

2)a where R is alkyl of from one to four carbon atoms. The catalystcomponents A and B are used in a molar ratio of from 1 l to 1 40 and thecomponents A and C are used in a molar ratio offrom 1 20.5 to l 100.

In a special embodiment of the invention a further amount ofhexa-alkylphosphoric acid triamide is added on completion of thehydrogenation of the polymer solution, whereafter the catalyst complexis destroyed by the addition of water (which may be acidified) and thecatalyst residues are separated together with the aqueous phase.

The addition of activator C to the hydrogenation mixture effects aconsiderable increase in the rate of hydrogenation, the duration ofhydrogenation being shortened'by about times. As compared with otheractivating additives, such as ethers, amines, or similarly stronglypolar solvents, the hydrogenation period is shortened by more than fourtimes. The process of the invention permits hydrogenation to be carriedout under considerably milder conditions, that is, at lower temperaturesand pressures. it also allows the catalyst concentration to be reducedconsiderably.

The addition of hexa-alkylphosphonc acid triamides moreover facilitatesthe remOval of the catalyst residues from the polymer solution, thiseffect being enhanced by a further addition of hexaalkylphosphoric acidtriamide on completion of the hydrogenation.

All polymers containing double bonds may be hydrogenated by the processof the invention. The polymers may have molecular weights of from 1,000to 1,000,000. The process is particularly useful for the hydrogenationof polymers of conjugated dienes, for example homo or co-polymers ofbutadiene, isoprene, 2,3-dimethylbutadiene, piperylene etc. Particularlyimportant copolymers in this class are those with vinyl compounds, forexample with styrene, substituted styrenes,

acrylonitrile, substituted acrylonitriles, and acrylates andmethacrylates. The copolymers may be random copolymers, block copolymersor segment copolymers in which one homopolymer block X is attached toone or two homopolymer blocks Y. Graft copolymers, for example those ofvinyl aromatic compounds on diene polymers, are also hydrogenatable. Theprocess of the invention is particularly advantageous in thehydrogenation of diene polymers produced by anionic solventpolymerization using organometallic catalysts such as lithiumalkyls.

In a preferred embodiment of the invention the hydrogenation is carriedout immediately after polymerization, in situ, in which case it is notnecessary for the polymerization catalyst to be destroyed or removedfrom the reaction mixture. The concentration of polymer in the solutionis from 1 to percent, preferably from 15 to 25 percent, by weight. Thehydrogenation of polybutadiene oils may, if desired, be carried out inthe absence of solvents.

Hydrogenation is carried out in solution in an inert organic solvent. Bythe term inert we mean that the solvent is not reactive with thereagents involved in the hydrogenation. Suitable solvents are, forexample, aliphatic hydrocarbons such as hexane or heptane, and etherssuch as diethyl ether or tetrahydrofuran. Aromatic hydrocarbons such asbenzene, toluene or ethyl benzene may only be used where thehydrogenation conditions are such that the aromatic double bonds are notattacked.

Component A of the catalyst complex consists of a compound of iron,cobalt or nickel. These metals may be present in either their divalentor trivalent forms. The anions may be both inorganic and organicresidues, preferred anions being chlorides, bromides, acetates,acetylacetonates and naphthenates. Most of these compounds are solublein organic solvents, but if this is not the case, fine dispersions maybe conveniently used.

Component B consists of an organo-aluminum compound. Preferred compoundsare aluminum trialkyls such as aluminum trimethyl, aluminum triethyl oraluminum triisobutyl. However, aluminum alkyl hydrides, aluminum alkylesters and aluminum alkyl halides are also suitable.

Component C acts as an activator on the catalyst complex A B. Itconsists of a hexa-alkylphosphoric acid triamide of the general formula:

2).-1 where R is alkyl of from one to four carbon atoms. We prefer touse hexamethylphosphoric acid triamide (HMPT).

The components A and B of the catalyst are used in a molar ratio of from1 40 to l l, and the components A and C are used in a molar ratio offrom 1 0.5 to l 100. The preferred ratio of A to B is from 1 20 to l 2,and the preferred ratio of A to C is from 1 l to 1 50. The optimumratios in any given case are governed by the nature of the components,and they may be determined by simple series of experiments. Where cobaltacetylacetonate is used as component A and aluminum tn'isobutyl is usedas component B the optimum ratio of A to B to C is, for example, about 19 6; where iron acetylacetonate is used as component A, the optimumratio is l 9 4; and where iron chloride is used as component A, theoptimum ratio is l :4 30.

The addition of the activator C to the catalyst complex makes itpossible to use very low catalyst concentrations.

Hydrogenation may be carried out at concentrations of less than 10' downto about 10" moles of component A per liter of solution.

The catalyst complex is prepared by mixing together the individualcomponents, conveniently in an inert organic solvent under a blanket ofinert gas such as N H or Ar and at temperatures between 20 and C. Thecomponents then react with each other to form the catalyst complex,usually as a deeply colored substance. It is believed that this reactioncauses the metal to change to a lower valency form, although itapparently does not separate in the metallic form but is held insolution by complex bonds or remains colloidally dispersed hydrogenatedor it can be stored for fairly long periods and used as required.

Hydrogenation is carried out with elementary hydrogen which isconveniently introduced into the polymer solution in the form of gas.Hydrogen pressures of from 1 to 200 atm are possible, although we preferto use pressures ranging from 1 to 50 atm. During hydrogenation thepolymer solution should be vigorously stirred to enable the hydrogen tocome into contact with the polymer as rapidly as possible. Thetemperature at which hydrogenation is carried out may be between -40 and+200 C, the preferred temperatures being in the range of 20 to 100 C.Since the catalyst complexes are prone to attack by oxygen, it isconvenient to operate in an atmosphere of hydrogen. The hydrogenationreaction proceeds very quickly, and it is usual for a 100 percenthydrogenation to be achieved in a few hours. We have observed thatterminal olefinic double bonds, that is, for example, double bondssituated at the ends of chains or on vinyl side groups, are hydrogenatedmore readily than intermediate double bonds, such as those occurring inthe 1,4-position in the polymerization of dienes. Thus selectivehydrogenation may be carried out if desired; if hydrogenation is stoppedprematurely, partial hydrogenation will occur, lateral vinyl groupsreacting preferentially, that is, they are the first groups to react.

If hydrogen is provided in adequate quantities, the hydrogenationproceeds up to a total degree of unsaturation of less than percent, thatis, at least 90 percent of the olefinic double bonds present in thepolymer are hydrogenated. The degree of unsaturation is measured byusual methods, such as infrared spectroscopy or iodine numberdeterminations Under mild reaction conditions aromatic double bonds suchas are present in copolymers of dienes and vinyl aromatic compounds arenot hydrogenated. However, aromatic double bonds will be hydrogenatedwhen the hydrogen pressure is raised, conveniently up to more than 10atmospheres, and when the molar ratio of component A to component B isrelatively high.

After hydrogenation the catalyst residues are removed from the polymersolution and the hydrogenated polymer is removed from the solution. Tothis end the catalyst complex is first of all destroyed by the additionof acidified water to the polymer solution. Then the aqueous phase isseparated from the organic phase. We have found that the catalystconstituents are more completely transferred to the aqueous phase andthat phase separation is improved when the catalyst complex containshexa-alkylphosphoric acid triamide. This effect is enhanced by addingfurther quantities of hexa-alkylphosphoric acid triamide to the polymersolution after hydrogenation is complete, as proposed in a specialembodiment of the invention. The polymer may then be isolated from thecatalyst-free polymer solution by usual methods, for example byevaporating the solvent or precipitating with methanol.

The resulting hydrogenated polymers are useful in the rubber industry oras plasticizers in the manufacture of impact-resistant thermoplastics.

EXAMPLE 1 a. Preparation of catalyst complex 1.7 g of cobaltousacetylacetonate and 7.5 ml of HMPT are dissolved in 14 ml of hexaneunder nitrogen and to the resulting solution there are added 76 ml of apercent solution of aluminum triisobutyl in hexane. The molar ratio of AB C is 1 9 6. Heat is generated and a deep brown catalyst solution isobtained.

b. Preparation of polymer 700 ml of butadiene are polymerized in 2,500ml of hexane in the presence of millimoles of n-butyl lithium at 70 C.Polymerization is complete after about 3 hours. There is thus obtained apolybutadiene having a molecular weight of about 175,000 and in whichabout 10 percent of the monomer units are in the 1,2-position.

c. Hydrogenation Hydrogenation is carried out in a stirred 5 litervessel in which the stirring speed is about r.p.m. (anchor agitator).

5 m1 of the solution of catalyst complex are added to the polymersolution. The concentration of catalyst component A in solution (b) is0.1 millimoles per liter. The mixture is then heated to 70 C. andhydrogen is passed in at a pressure of 4.5 atmospheres. 50 percent ofthe double bonds are hydrogenated in the first 0.2 hour, and thehydrogenation is virtually complete after 1 hour (the measurement of thedegree of unsaturation is effected by infrared spectroscopy using smallsamples taken from the reaction vessel at intervals of 5 minutes).

d. Isolation of hydrogenated polymer To the polymer solution there areadded 50 ml of HMPT followed by 200 ml of water. The mixture is thenvigorously stirred for 5 minutes at 50 C., and a further 200 ml of waterare added. The mixture is allowed to stand, and the aqueous phasegradually separates from the organic phase. The aqueous phase isdecanted from the organic phase and the latter is distilled in vacuo toremove the solvent. The polymeric residue is dried. This comprises apolyethylene having about 10 percent of lateral ethyl groups. Itcontains less than 2 ppm of cobalt and 2 ppm of aluminum.

EXAMPLE 2 (Comparative Example) A catalyst complex is prepared asdescribed in Example 1a but without the addition of HMPT. Polybutadieneis prepared as described in Example lb and hydrogenated as described inExample 1c. Hydrogenation of the first 50 percent of the double bondstakes 5 hours and the hydrogenation of all of the double bonds takes 30hours.

EXAMPLE 3 (Comparative Example) Catalyst preparation, polymerization andhydrogenation are carried out as described in Example la, lb and lc. Inworking up the product, however, no further HMPT is added. The finalproduct contains 200 ppm of cobalt and 20 ppm of aluminum. It is coloredbrown and shows poor resistance to aging,

EXAMPLE 4 In two parallel polymerization charges 75 ml portions ofstyrene are polymerized in 2,000 ml of toluene in the presence of 15millimoles of n-butyl lithium at 40 C. After 30 minutes 400 ml ofbutadiene are added, the temperature rising to 50 to 60 C.Polymerization of the butadiene is complete after 3 hours. A further 25ml of styrene are then added and polymerization is resumed for 30minutes at 40 C. There is thus obtained a three-block copolymer ofstyrene/butadiene/styrene.

To one of the polymer solutions there are added 5 ml of the catalystsolutions prepared as described in Example la and to the other polymersolution there are added 5 ml of the catalyst solution prepared asdescribed in Example 2. In each case hydrogenation is effected at 25 C.using a hydrogen pressure of 4.5 atmospheres. ln the charge containingthe catalyst complex of the invention 50 percent of the double bonds arehydrogenated after 0.25 hour and all of the olefinic double bonds arehydrogenated after 1.3 hours; in the comparative test not making use ofHMPT additive hydrogenation of the first 50 percent of the double bondstakes 6 hours and that of all of the double bonds 35 hours.

EXAMPLE 5 300 ml of styrene and 460 ml of butadiene are dissolved in2,500 ml of toluene and polymerized in the presence of 9 millimoles ofn-butyl lithium at 40 to 60 C. during 3 hours. There is obtained atwo-component block copolymer, the first block consisting ofpolybutadiene containing about 10 percent of styrene in randomdistribution, and the second block consisting of pure polystyrene.

To the polymer solution there are added 5 m1 of the catalyst solutionprepared as described in Example la and hydrogenation is effected at 25C. using a hydrogen pressure of 3.5 atmospheres. Hydrogenation of thefirst 50 percent of the double bonds takes 0.2 hour and that of 100percent of the double bonds takes l hour.

The steric configuration of the polybutadiene block was determined inthe non'hydrogenated state (100 percent unsaturation) and in thesemi-hydrogenated state (50 percent unsaturation), the results being asfollows:

TABLE 1 Unsaturation 1,2 portions 1,4-cis 1,4-trans 100 10 35 55 50 2030 It is evident that the 1,2-vinyl side groups are preferentiallyhydrogenated.

The polymer solution was worked up as described in Example 1d with theaddition of HMPT. The isolated hydrogenated two-component blockcopolymer was subjected to mechanical properties tests and the resultscompared with those obtained in tests on a non-hydrogenatedtwo-component control Solutions of catalyst complexes were prepared asdescribed in ExamPle la with the addition of HMPT but using, in place ofcobalt acetylacetonate, equimolar amounts of iron and nickelacetylacetonates. Two-component block copolymers of styrene andbutadiene were prepared as described in Example and then hydrogenatedwith 5 ml of the catalyst solutions in each case. Table 3 gives thehydrogenation times in hours:

TABLE 3 Catalyst 50% Hydrogenated 100% Hydrogenated Fe AcAc 2.5 14 hoursNi AcAc 2.0 12 hours Co AcAc 0.2 1 hour EXAMPLE 7 Solutions of catalystcomplexes were prepared as described in Example la using different molarratios of the components A and C. Two-component block copolymers ofstyrene and butadiene were hydrogenated as described in Example 5. Table4 gives the hydrogenation times in hours for the various ratios of A toC.

Solutions of catalyst complexes were prepared as described in Example lausing various ratios of A to B to C. Two-component block copolymers werehydrogenated as described in Example 5. Table 5 gives the hydrogenationtimes in hours.

TABLES Ratio A B C 50% Hydrogenated 100% Hydrogenated 1 :4 6 1.0 4.0 1:9 6 0.2 1.0 l 18:6 1.1 4.2 l :4: 10 0.3 1.5 l :9: 10 2.0 12.5 1 18: 100.2 1.1

EXAMPLE9 a. A catalyst complex was prepared from 1.7 g of ironacetylacetonate, 76 ml of a 20 percent solution of aluminum triisobutyland various quantities of HMPT.

A two-component block copolymer was hydrogenated as described in Example5 but using a pressure of 4.5 hydrogen atmospheres and a temperature of40 C. Table 6 gives the hydrogenation times in hours for the variousmolar ratios:

TABLE 6 Ratio A B C 50% Hydrogenated 100% Hydrogenated It will be seenfrom the Table that where iron acetylacetonate is used as component Aless l-lMPT is required to achieve optimum hydrogenation times than whencobalt acetylacetonate is used.

EXAMPLE 10 Solutions of catalyst complexes were prepared as described inExample la but using, in place of HMPT, equimolar amounts of other polarcompounds.

Two-component block copolymers were hydrogenated as described in Example5. Table 7 gives the hydrogenation times in hours.

TABLE 7 Additive 50% Hydrogenated 100% Hydrogenated None 4.0 25 HMPT(invention) 0.2 1.0 dimethyl sulfoxide 1.9 9.5 dimethyl formamide 2.510.0 diethyl ether 2.2 8.0 dioxane 1.0 4.0 trimethylamine 1.2 5.8tributyl phosphite 2.0 8.5 tributyl phosphate 2.5 10

EXAMPLE 1 l A solution of a catalyst complex was prepared from 1.7 g ofcobalt acetylacetonate, 60 ml of hexane, 5 ml of HMP'T and 30 ml of a 20percent solution of aluminum trimethyl in hexane. The molar ratio of thecomponents A to B to C is l 3.8 4. A two-component block copolymer ofstyrene and butadiene was produced as described in Example 5 but usingelevated hydrogen pressure (about 100 atmospheres) and elevatedtemperature (80 C). Hydrogenation was stopped after 6 hours, and theproduct was then analyzed. No olefinic double bonds and only 10 percentof the aromatic double bonds were found.

EXAMPLE 12 A solution of a catalyst complex was prepared from 0.85 g offerrous chloride, 42.5 ml of hexane, 42.5 ml of HMPT and 32.5 ml ofaluminum triisobutyl. The molar ratio of A to B to C was 1 :4: 35.

A two-component block copolymer was hydrogenated using ml of the abovesolution (equivalent to 0.2 millimoles of iron per liter). Half of thedouble bonds were hydrogenated after 0.3 hour and all were hydrogenatedafter 1.4 hours.

What we claim is:

l. A process for the catalytic hydrogenation of polymers containingdouble bonds by the action of hydrogen on a solution of the polymer inan inert organic solvent and in the presence of a catalyst complexconsisting of:

A. a compound of iron, cobalt or nickel,

B. an organo-aluminum compound and C. an activator,

wherein the activator used is a hexa-alkylphosphoric acid triamide ofthe general formula:

)a in which R is alkyl of from one to four carbon atoms, the componentsA and B being used in a molar ratio of from 1 40 to l l and thecomponents A and C in a molar ratio of from 1 0.5 to l 100.

2. A process as claimed in claim 1 wherein a further quantity ofhexa-alkylphosphoric acid triamide is added to the polymer solutionafter completion of hydrogenation, whereupon the catalyst complex isdestroyed by the addition of 0p tionally acidified water and thecatalyst residues are removed together with the aqueous phase.

* l I! i 3, 75, Dated June 27, 1972 Patent No.

Inventofls) Klaus Bronsterc et 211 It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

First Page, left-hand column, "P 19 15 263.2" should read Column 1, line64, "remOval Should read removal Column 4, line 50, "25" should read, 75

Column 5, line 57 "ExamPle" should read Example Signed and sealed this19th day of December 1972.

(SEAL) Attest:

EDWARD M.F'LETCHER,JR. ROBERT'GOTTSCHALK Attesting Officer Commissionerof Patents

2. A process as claimed in claim 1 wherein a further quantity ofhexa-alkylphosphoric acid triamide is added to the polymer solutionafter completion of hydrogenation, whereupon the catalyst complex isdestroyed by the addition of optionally acidified water and the catalystresidues are removed together with the aqueous phase.